The present invention generally relates to techniques for use in magnetic recording systems and, more particularly, to techniques for performing servo data detection in the presence of radial incoherence.
A read channel integrated circuit (IC) is one of the core electronic components in a modem magnetic recording system such as a hard disk drive. A read channel converts and encodes data to enable the heads to write data to the disk drive and then read back the data accurately. The disks in a drive typically have many tracks on them. Each track typically consists of mostly user or xe2x80x9creadxe2x80x9d data sectors, as well as control or xe2x80x9cservoxe2x80x9d data sectors embedded between the read sectors. The servo sectors help to position the magnetic recording head on a track so that the information stored in the read sectors is retrieved properly.
A typical magnetic recording system includes some mechanism for detecting servo data. However, a problem that inhibits the ability of such a detecting mechanism to reliably detect servo data during a disk seek is a condition referred to as xe2x80x9cradial incoherence.xe2x80x9d Radial incoherence (RI) refers to the offset in timing between radially adjacent servo tracks. From a signal processing point of view, quick phase changes and some signal loss are characteristics of RI.
Thus, in magnetic recording systems, there is a need for techniques which improve servo data detection performance in the presence of radial incoherence.
The present invention provides techniques for detecting control data, such as servo data, from input or incoming data read from a magnetic recording medium, preferably in the presence of radial incoherence. More specifically, the techniques employ multiple (i.e., two or more) data detectors for choosing between multiple sampling phases associated with the input data read from the magnetic recording medium.
In one aspect of the invention, such a technique for detecting control data from input data stored on a recording medium comprises the following steps. First, the input data read from the recording medium is respectively sampled at two or more predetermined phases, i.e., samples are respectively generated from the input data at the two or more predetermined phases. The input data sampled at the two or more predetermined phases is then respectively applied to two or more data detectors. Then, output data from one of the two or more data detectors is identified as detected control data based on a predetermined detection criterion.
In the context of servo data detection, the predetermined detection criterion comprises identifying output data from the first data detector to detect a servo address mark in the input data. The two or more predetermined phases used to sample the input data may comprise a nominal phase and at least one phase other than the nominal phase. In one embodiment, the at least one phase other than the nominal phase is spaced T apart from the nominal phase, where T is a nominal spacing associated with input samples. In another embodiment, the at least one phase other than the nominal phase is spaced a multiple of T apart from the nominal phase. In yet another embodiment, the at least one phase other than the nominal phase is spaced a fraction of T apart from the nominal phase. Still further, the two or more data detectors may be partial response maximum likelihood detectors such as Viterbi decoders.
Such servo detection techniques offer several orders of magnitude in performance improvement in detecting servo data in the presence of RI and may advantageously be employed in a read channel integrated circuit. Furthermore, such techniques may be applied to any servo encoding system.
Advantageously, for a given level of performance, the servo data detection techniques of the present invention improve seek time in magnetic recording systems. That is, since the techniques of the invention handle radial incoherence effectively, faster disk seeks are possible. Also note that for a given level of performance, tracks can be written closer and the disks can be spun faster with the application of techniques of the present invention. Thus, as will be explained in detail below, the invention advantageously exploits the use of multiple data detectors in the presence of quick phase changes in order to provide improved servo data detection performance.
It is to be understood that since writing data to, storing data in, and reading data from a magnetic recording medium may be considered a transmission channel that has an associated frequency response, the techniques of the present invention are more generally applicable to any digital transmission systems such that detection of digital data represented by a sequence of symbols, where each symbol may be made up of a group of bits, may be improved.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.